Evidence of phase resetting, not just pulses of sound, during eye movement-related eardrum oscillations (EMREOs)

Eye movement-related eardrum oscillations (EMREOs) appear to consist of a pulse of oscillation occurring in conjunction with saccades. However, this apparent pulse could occur either because there is an increase in energy at that frequency at the time of saccades (a true pulse), or because there is saccade-related phase resetting of ongoing energy at that frequency band, thus appearing like a pulse when averaged in the time domain across many trials. Here we conducted a spectral analysis at the individual trial level in humans performing a visually guided saccade task to determine whether the power at the EMREO frequency (30-45 Hz) is higher during saccades than during steady fixation. Although all subjects had easily identifiable EMREOs, we found that only 40% of participants showed a statistically significant increase in sound power in the EMREO frequency band associated with saccade onset, i.e. sound pulses at the individual trial level (in some cases, these power increases were sustained during eccentric fixation). In contrast, 97% of subjects showed statistically significant phase resetting at saccade onset. While both factors may contribute to the apparently pulse-like EMREO signal, phase resetting appears to be more reliably associated with EMREOs. The prevalence of phase resetting has implications for the underlying mechanism(s) producing EMREOs as well as functional consequences for how the ear might respond to incoming sound in an eye-position dependent fashion.